The present invention relates generally to pumps and hydraulically-actuated systems used with internal combustion engines, and more particularly to axial hydraulic pumps with wobble plates.
Hydraulic pumps that utilize wobble plates to drive reciprocating pistons are susceptible to wear. The wobble plate is usually the drive plate with a tilted pumping surface that pushes against the pump""pistons. As the drive plate rotates each piston is pushed away from the drive plate as the thickness of the drive plate beneath it becomes greater with the rotation, causing the piston to compress. The hydraulic pressure within the piston increases as the volume within the piston decreases. This high pressure hydraulic fluid is generally the output product of the hydraulic pump. As rotation continues and the thickness of the drive plate beneath the piston lessens, the higher hydraulic pressure within the piston allows it to expand again and refill itself with lower pressure hydraulic fluid.
There is generally friction between the drive plate and the piston as the drive plate rotates. This can cause wear to the piston and drive plate surfaces. Additionally, there is generally friction and wear against other surfaces that the rotating drive plate comes in contact with, as well.
Of course, the drive plate and whenever holds it must also be capable of bearing the loads caused by pushing against the compressing pistons. These loads may be axial (i.e., parallel to the drive shaft axis and/or perpendicular to the plaintiff rotation of the drive plate) or radial (i.e., perpendicular to the drive shaft axis), or some combination thereof.
In one aspect of the invention, a displacement pump comprises a rotatable drive shaft; a low-pressure hydraulic fluid reservoir; at least one piston containing a piston cavity; and a drive plate connected with the drive shaft. The drive plate includes an inlet passage and a fill slot. The fill slot is fluidly connected with the low pressure hydraulic fluid reservoir via the inlet passage. The drive plate is rotatable about the drive shaft such that as the drive plate rotates the piston cavity is intermittently fluidly connected with the fill slot.